The disclosed technology relates to communications systems, and more particularly, to performing successive interference cancellation (SIC) in communications systems with or without retransmissions.
In a data transmission system, it is desirable for information, often grouped into packets, to be accurately received at a destination. A transmitter at or near the source sends the information provided by the source via a signal or signal vector. A receiver at or near the destination processes the signal sent by the transmitter. The medium, or media, between the transmitter and receiver, through which the information is sent, may corrupt the signal such that the receiver is unable to correctly reconstruct the transmitted information. Therefore, given a transmission medium, sufficient reliability is obtained through careful design of the transmitter and/or receiver, and of their respective components.
Successive interference cancellation (SIC) is a technique for improving the performance of a data transmission system. According to this technique, a received codeword that is associated with a small amount of corruption (e.g., due to favorable channel conditions), is decoded before other codewords that are associated with larger amounts of corruption. Effects of the decoded codeword are subtracted from a received signal vector to eliminate interference due to the decoded codeword from the other codewords. In this way, the other codewords may experience less interference and are able to achieve a high signal-to-noise ratio (SNR) than without interference cancellation.
The order in which codewords are decoded is an important design consideration. Conventional SIC methods decode codewords in an order that is based on information that reflects long-term channel conditions or channel performance, such as a long-term signal-to-noise ratio. However, because channel and interference conditions may change rapidly, such information may not accurately reflect the conditions pertaining to a specific transmission attempt (e.g., in a specific subframe of the communication system).